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  • Hierarchical classifier constructing problems for radio-photon sensor systems based on addressable fiber Bragg structures

    Radio-photon sensor systems represent a wide range of measurement information systems that use today's standardized parallel and sequential type optical analog chains with filtering, which allows to functionally display information received in the optical range in the radio frequency. One of the main, most widely used elements in the RPSS, which solves the problems of forming, filtering and measuring the conversion of optical radiation, including for the stage of further generation of radio-frequency carriers, is the fiber Bragg grating. The cumulative analysis made it possible to propose for the design of RFSSS a new class of sensors - address fiber Bragg structures (AFBS) constructed on the basis of FBG with two symmetrical discrete phase shifts or two identical FBGs potentially having improved metrological and technical and economic characteristics, as well as enhanced functionality compared with existing, widely used resonance sensors, based on the effects of Bragg and Fabry-Perot in fiber optics. AFBS, by its designation, should become a multifunctional element of the RPSS that act as sensors, formers of two-frequency optical radiation, the basis for generating in each of them a unique difference radio frequency carrying measurement information, which is also the address for their multiplexing. This made it possible to propose a new, separate class of the RPSS, which was named "Radiophotonic sensor systems on adressed fiber Bragg structures", the hierarchical classifier for the creation of which was the main subject of this article.

    Keywords: radio-photon sensor system, addressed fiber Bragg structure, integrated fiber-optic sensor, interrogation, multiplexing, hierarchical classifier of construction problems, system approach

  • Address fiber Bragg structures based on two identical upper-band gratings

    The multi-advantageous fiber Bragg gratings (FBG) have attracted considerable interest from developers of various optical systems, including communication systems with spectral and code multiplexing, as well as fiber-optic and radio-photon sensor systems. The complexity and high cost of multiplexing and interrogation of complex fiber-optic sensors (CFOS) is still the main limitation for the widespread introduction of sensory systems, both distributed and quasi-distributed, and point-type.This article proposes a new multiplexing method that takes advantage of both broadband fiber-optic and dual-frequency or polyharmonic radio-photon sensor systems. The simplest broadband radiator is taken from the first, but a complex and expensive system of spectrometry is not used to determine the central wavelength of the FBG. From the second, a recording system is used at the beat frequency between two components, but an expensive system for generating two- or polyharmonic sounding systems is not used. The multiplexing parameter is determined by the frequency of separation between two identical over-narrow-band FBGs, which differs by a certain amount from each of the CFOS and, in fact, generates its address. At the same time, FBG-based structures remain a sensitive element of the systems. Thus, a new class of sensitive elements is formed - address fiber Bragg structures (AFBS).

    Keywords: radio-photon sensor system, address fiber Bragg structure, integrated fiber-optic sensor, interrogation, multiplexing, two identical over-narrow-band fiber Bragg gratings, frequency spacing, address

  • Characterization of Fano resonance in optical biosensors of refractometric type based on ring fiber Bragg gratings with pi-shift. Statement of modeling tasks

    A variant of the solution of the problem of characterization of a resonant Fano contour in optical biosensors of refractometric type based on ring fiber Bragg gratings with pi-shift is presented. The use of biosensors of this type makes it possible to increase the sensitivity of detecting changes in the refractive index of the medium under investigation to the level (1-2) x10-9 RIU. These sensitivity values are achieved due to the formation in the lattice of a high-quality Fano resonance with a loop width at half-height equal to 1-5 pm. However, the possibility of obtaining a significant gain in metrological characteristics on the one hand, poses the problem of characterizing such narrow-band resonances on the other, since the existing optical spectrum analyzers do not have the appropriate resolution. To solve this problem, we propose a radio-photon method of three-frequency probing of a high-band and an asymmetric Fano contour by symmetric amplitude-modulated radiation with side-amplitude components unbalanced in amplitude. In contrast to the previously used for solving similar problems of two-frequency symmetric sounding with equal amplitudes of side components and a suppressed carrier, we have uniquely determined the central frequency, the maximum amplitude and Q of the Fano circuits, as well as the possibility of greatly simplifying the technique of collecting information on their parameters. The article consists of two parts, which consistently reflect the posing of modeling problems and discussing its results with confirmation of the results of physical experiments.

    Keywords: optical biosensor, refractometry, Bragg fiber grating, phase pi-shift, Bragg annular fiber grating with phase pi-shift, Fano resonance, refractive index change, sensitivity, resolving power, radiophoton measurement methods, two-frequency symmetric balance

  • Characterization of Fano resonance in optical biosensors of refractometric type based on ring fiber Bragg gratings with pi-shift. Statement of modeling tasks

    A variant of the solution of the problem of characterization of a resonant Fano contour in optical biosensors of refractometric type based on ring fiber Bragg gratings with pi-shift is presented. To solve this problem, the first part of the article proposes a radio-photon method of three-frequency probing of the upper-band and asymmetric Fano contours by symmetric amplitude-modulated radiation with amplitude components unbalanced in amplitude. To characterize the central wavelength, a functional analogous to the modulation coefficient of the beat envelope between the components of the probing radiation is introduced. The requirements for the selection of the frequencies of the side components at which the uniqueness of the functional is preserved and the maximum sensitivity in the measurement range determined by the bandwidth of the Fano contour at half-height are justified. The possibility of extending the range of lateral frequencies and increasing the sensitivity of measurements with the use of two-frequency sounding with a frequency reduced by half and amplitude unbalanced side components with a suppressed carrier is shown. An example is given of a comparison with the two-frequency symmetric probing, previously used by us for solving similar problems, with equal amps of side components and a suppressed carrier. Based on the results of characterizing the Fano contour with fixed probing, it is possible to unambiguously determine the central frequency, the maximum amplitude, and its Q-factor.

    Keywords: optical biosensor, refractometry, Bragg fiber grating, phase pi-shift, Bragg annular fiber grating with phase pi-shift, Fano resonance, radio-photon measurement methods, amplitude-balanced three-frequency symmetric probing, two-frequency disbalanced and a